The present invention relates to methods for applying a desired shape to archwires to be used in orthodontic appliances for the straightening of teeth, and more particularly, to the automated manufacture of customized archwires using robotic devices.
The common approach for orthodontic appliances is to bond small metallic parts (“brackets”) onto the outer (“labial”) side of the teeth, and to insert a wire into the slots of the brackets. The wires are typically preformed off-the-shelf wires, and the brackets are bonded basing on visual judgment by the orthodontist. However, the use of computerized processes in orthodontics increases. Especially when the brackets are bonded to the back side of the teeth (“lingual orthodontics”), the use of computer assisted processes for designing the brackets and manufacturing the wires has achieved a significant market share. Using computerized processes typically results in providing a numeric description of an orthodontic archwire.
Devices for bending orthodontic archwires have been proposed in the prior art. In U.S. Pat. No. 5,431,562, Andreiko et al. describes an apparatus that takes a straight archwire and imparts a simple planar arcuate curvature to the wire. However, the Andreiko et al. wire bending apparatus cannot produce any complex and twists bends in the wire, e.g., bends requiring a combination of translation and rotational motion.
In U.S. Pat. No. 6,612,143 (“Robot and method for bending orthodontic archwires and other medical devices”), Butscher et al. discloses a robot capable of bending fully three-dimensional orthodontic archwires. The device comprises two grippers, one of the grippers being mounted to a six-axis-robot arm and thus moveable. The gripping tools preferably incorporate force sensors which are used to determine overbends needed to get the desired final shape of the archwire. The manufacturing process uses straight pieces of wire and step by step applies bends and/or twists to the wire, thus forming an archwire. The process as described in the '143 patent requires the calculation of the consumed wire length for a bend. Even a slight miscalculation of the consumed wire length for a bend generates significant forces along the longitudinal axis of the wire. Those high forces arising by estimating an improper consumed wire length for a bend will superimpose the bending forces and significantly disturb the desired measurements of those forces.
The patent to Orthuber et al., U.S. Pat. No. 4,656,860 also describes a bending robot for bending archwires. A robot as described in the '860 patent was manufactured and sold as part of a complete orthodontic solution by Geyer Medizintechnik GmbH in Berlin, Germany, but never widely commercialized. The robot consisted of two characteristic design features: a bending cone that could move forwards and backwards to bend the wire, and a rotating cone that could twist the wire. As such, it could only apply torque or bends over the two main axes of a cross section of a rectangular shaped wire. Basing on the embodiment distributed by Geyer Medizintechnik GmbH, a series of three twists and two bends were required to shape an archwire so that it would fit in the slots of two adjacent brackets. This series of twists and bends required as much as 5 mm of wire length between adjacent brackets. This length of wire is greater than that available for closely spaced teeth, especially in lingual orthodontics.
The present invention presents substantial improvements over prior art as disclosed in the cited applications.